Now that I looked at your site heather, I think i know what the op is looking for. There is a “since last visit” (or something) plugin out there somewhere. If im not mistaken podz uses it. Might want to hunt around for that..

Thanks for this. Unfortunately I get:
Warning: main(/wp-content/plugins/wp-last-visit.php?type=js): failed to open stream: No such file or directory in /usr/www/users/mhains/hainsworth/wp-content/themes/fresh/header.php on line 5

when I place the necessary code in the header.php — the instructions say put it in the head portion of your index.php, but it appears this plug-in was written for v1.2 of WordPress and the head tag has been moved to header.php since.